/*
 * @Author: 肖思汗 
 * @Date: 2025-06-16 14:04:06 
 * @Last Modified by:   肖思汗 
 * @Last Modified time: 2025-06-16 14:04:06 
 */

// @ts-nocheck

/**
 * Implementation of atob() according to the HTML and Infra specs, except that
 * instead of throwing INVALID_CHARACTER_ERR we return null.
 */
export default function atob(data) {
    // Web IDL requires DOMStrings to just be converted using ECMAScript
    // ToString, which in our case amounts to using a template literal.
    data = `${data}`;
    // "Remove all ASCII whitespace from data."
    data = data.replace(/[ \t\n\f\r]/g, '');
    // "If data's length divides by 4 leaving no remainder, then: if data ends
    // with one or two U+003D (=) code points, then remove them from data."
    if (data.length % 4 === 0) {
        data = data.replace(/==?$/, '');
    }
    // "If data's length divides by 4 leaving a remainder of 1, then return
    // failure."
    //
    // "If data contains a code point that is not one of
    //
    // U+002B (+)
    // U+002F (/)
    // ASCII alphanumeric
    //
    // then return failure."
    if (data.length % 4 === 1 || /[^+/0-9A-Za-z]/.test(data)) {
        return null;
    }
    // "Let output be an empty byte sequence."
    let output = '';
    // "Let buffer be an empty buffer that can have bits appended to it."
    //
    // We append bits via left-shift and or.  accumulatedBits is used to track
    // when we've gotten to 24 bits.
    let buffer = 0;
    let accumulatedBits = 0;
    // "Let position be a position variable for data, initially pointing at the
    // start of data."
    //
    // "While position does not point past the end of data:"
    for (let i = 0; i < data.length; i++) {
        // "Find the code point pointed to by position in the second column of
        // Table 1: The Base 64 Alphabet of RFC 4648. Let n be the number given in
        // the first cell of the same row.
        //
        // "Append to buffer the six bits corresponding to n, most significant bit
        // first."
        //
        // atobLookup() implements the table from RFC 4648.
        buffer <<= 6;
        buffer |= atobLookup(data[i]);
        accumulatedBits += 6;
        // "If buffer has accumulated 24 bits, interpret them as three 8-bit
        // big-endian numbers. Append three bytes with values equal to those
        // numbers to output, in the same order, and then empty buffer."
        if (accumulatedBits === 24) {
            output += String.fromCharCode((buffer & 0xff0000) >> 16);
            output += String.fromCharCode((buffer & 0xff00) >> 8);
            output += String.fromCharCode(buffer & 0xff);
            buffer = accumulatedBits = 0;
        }
        // "Advance position by 1."
    }
    // "If buffer is not empty, it contains either 12 or 18 bits. If it contains
    // 12 bits, then discard the last four and interpret the remaining eight as
    // an 8-bit big-endian number. If it contains 18 bits, then discard the last
    // two and interpret the remaining 16 as two 8-bit big-endian numbers. Append
    // the one or two bytes with values equal to those one or two numbers to
    // output, in the same order."
    if (accumulatedBits === 12) {
        buffer >>= 4;
        output += String.fromCharCode(buffer);
    } else if (accumulatedBits === 18) {
        buffer >>= 2;
        output += String.fromCharCode((buffer & 0xff00) >> 8);
        output += String.fromCharCode(buffer & 0xff);
    }
    // "Return output."
    return output;
}
/**
 * A lookup table for atob(), which converts an ASCII character to the
 * corresponding six-bit number.
 */

const keystr =
    'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/';

function atobLookup(chr) {
    const index = keystr.indexOf(chr);
    // Throw exception if character is not in the lookup string; should not be hit in tests
    return index < 0 ? undefined : index;
}
